Fluorinated elastomer blends

ABSTRACT

A fluoroelastomer combination is provided having improved processing and handling characteristics. The fluoroelastomer combination comprises at least two highly fluorinated elastomeric polymers, one of said polymers being dispersed throughout a continuous phase of the other of said polymers.

United States Patent [191 Stivers rm j3,723, 577 [451 Mar.'27,19 73 [s41 FLUORINATED ELASTOMER BLENDS [75] Inventor: David A. Stivers, Saint Paul,

[73] Assignee: Minnesota Mining and Manufacturing Company, St. Paul, Minn.

[22] Filed: Nov. 5 1970 21 App]. NOl: 87,359

[52 U.S.Cl. ..260/900, 260/235 R, 260/41 A,

' 260/41 B, 260/41 R, 260/827, 260/859 R 51] inn-cl. ..c0s'f29/22 [58] FieldofSearch ..260/900, 92.18, 899, 827,

[56] References Cited UNITED STATES PATENTS 3,142,660 7/1964 COngeI..... ..260/47 phase of the other of said polymers.

Kaufman ..260/45.5

3,030,260 4/ 1962' Metzler et a]. 156/305 3,025,183 3/1962 Yuan 117/126 3,019,206 1/ l 962 Robb.. 260/296 2,854,699 10/1958 Robb 18/55 3,560,595 2/ 1971 Phillips et a1 ..260/900 Primary Examiner-Samuel H. Blech Assistant Examiner- C. J. Seccnro Attorney-Kinney, Alexander, Sell, Steldt & Delahunt s Cla'inm, No Drawings FLUORINATED ELASTOMER BLENDS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to fluorinated elastomers and, more particularly, to blends of fluorinated elastomers.

2. Description of the Prior Art:

Elastomeric fluorinated polymers of various types have been known for some time, e.g., see U.S. Pat. Nos. 2,752,331, 2,968,649, 3,051,677, 3,318,854, 3,331,823, and 3,179,619. These elastomeric polymers are very useful because of their desirable chemical and physical properties, e.g., chemical resistance and thermal stability. Certain of these elastomeric polymers also have other very desirable properties such as good tear strength, good tensile strength and elongation, etc.

Generally, when polymers are blended together, the resulting mixture exhibits properties which are a weighted average of the corresponding properties of the starting polymers. Thus, an improvement in one property is usually obtained at the expense of another desirable property.

Although blends of certain fluorinated polymers have been described, e.g., see U.S. Pat. Nos. 2,789,959, 2,789,960, 2,927,908, 3,019,206, 3,075,939, 3.l05,827, 3,291,864, and 3,484,503, such blends have not suggested the fluoroelastomer combination of my invention.

SUMMARY OF THE lNVENTlON In accordance with the invention an elastomeric fluorinated polymer is modified with another elastomeric fluorinated polymer so as to provide a fluoroelastomer combination which, without significant loss of thermal stability or solvent resistance, has a balance of physical characteristics superior to those of either starting elastomer and which, since the components are all elastomeric in nature, can be readily processed over a wide range of respective elastomer concentrations.

Thus, there is provided a thermally stable, chemicalresistant fluoroelastomer combination of improved processing and handling properties comprising at least two highly fluorinated elastomeric polymers. The first of said polymers is in the form of a continuous phase and at least one other polymer is dispersed throughout said first polymer.

Useful highly fluorinated elastomeric polymers are those which contain at least 37 percent by weight of carbon-bonded fluorine and, preferably, those polymers in which at least SOpercent of the nonskeletal carbon valence bonds are to fluorine. The useful polymers are those which are elastomeric. For this purpose I adopt the definition of elastomer contained in ASTM Special Technical Publication No. 184 (1956). Elastomer is defined there as a substance that can be stretched at room temperature to at least twice its original length, and, after having been stretched and the stress removed, returns with force to approximately its original length in a short time.

The useful highly fluorinated elastomeric polymers can be prepared by condensation reactions, e.g., to form polymers such as fluorosilicones, (e.g. based on FsCHzonz asixniiihie x is OH or c1 fluorinated urethanes, fluorinated polyesters (e.g. based on HOCH,(CF,),CH,OH), and the like; they can also be prepared by addition reactions. Preferred elastomeric addition polymers are the saturated polymers derived from mono-ethylenically unsaturated (vinyl) monomers or fluoroalkyl nitroso monomers. Monomers useful in preparing elastomeric addition polymers include:

One preferred embodiment of the invention comprises a thermally stable, chemical-resistant fluoroelastomer combination of improved processing and handling properties which comprises at least two highly fluorinated elastomeric polymers wherein one of said polymers is chlorine-free and another of said polymers is chlorine-containing. One of the polymers is in the form of a continuous phase and another of the polymers is dispersed throughout the continuous phase polymer.

By chlorine-free polymer I mean that the highly fluorinated elastomeric polymer does not contain a significant amount of chlorine, i.e., less than about one weight percent. Examples of preferred chlorine-free poly n ers are those elastomeric copolymers pf CF CHz/CFaCF CFz/CFz C1 CF CHz/ CF CF CFg and CF CH2/CF CF =CFH. An example of a chlorine-containing polymer is an elastomeric copolymer of CF2=CH2 and CF =CFCL The fluoroelastomer combination can include from about 3 to about 97 weight percent of the chlorine-containing polymer. Generally, for improving tear strength of the chlorine-free polymer, concentrations of 3 to 30 weight percent of the chlorine-containing polymer are preferred and concentrations of about 5 to-20 weight percent are even more preferred. The processing and handling, i.e. calendering, extruding, molding, etc.,.of the chlorine-containing polymer are improved by dispersing therethrough about 3-40 weight percent or more of a chlorine-free polymer without the loss of advantageous properties such as solvent resistance, thermal stability, resistance to aging, which occurs when conventional processing aids are used.

When each of the' highly fluorinated elastomeric polymers are to be cured and reinforced by the same compounding agents, one method of preparing the fluoroelastorner combination is by mixing or compounding the desired curable polymer gum stocks together in the desired proportions by using any of the usual rubber mixing devices, such as Banbury mixers, roll mills, or any other convenient mixing device. After the polymer gum stocks have been so blended, the modifying agents, pigments, reinforcing agents and curatives may be added to the blended elastomeric polymers. It is also possible, and generally preferred, to first blend the desired pigments, modifying agents, reinforcing agents and curatives into each of the curable elastomeric polymers separately before the polymers cured) all a temperature beiwcfin about 300 F- are blended with each other. Using this latter method and about usually at about permits one to use different amounts and types of cura l b-H of from 2 ing agents and fillers in each type of elastomeri hours to 50 hours depending on the cross-sectional polymer. thickness of the sample. I

For the blending it has been found that a two-roll v The following examples are provided to-illustrate the rubber mill equipped with heat exchange means, e.g., present invention and are not to be construed as limitcored chambers for cooling, is particularly suitable l"! the QPQ E since the heat generated by the high shearing forces in lo mixing can be dissipated and the temperature more ac- To illustrate the advantages g increased tear curately regulated with this device or with devices strength) obtained by blending varying amounts of a providing other means for temperature control. For highly fluorinated, chlorine comaining elastomefic best results the temperature of the material on the mill polymer with a highly fl ri t d hl i f e is not allowed to rise above about and elastomeric polymer, the formulations shown in Table I is not allowed to fall below 30 F. (0 C.). During were prepared. Formulations 1, 2 and 11 were milling it is desirable to uniformly disperse one or more prepared by blending all of the stated ingredients of the elastomeric ol mers th h another together on a two-roll rubber mill. Each of the remainelastomeric polymer. However, prolonged milling is mg formulations was Prepared first blending not desirable after the elastomeric polymers have been together F a the ingredients which are adequately mixed Thus, it is not necessary that the marked with an asterisk and then blending together, as

dispersion be in the form of a solution of one polymer gg gg g z s fi ig g zg i f gi t z in another. For example, it has been observed that a p e e e e g thin film cast from a solution of an elast m fluoroelastomer combination comprising the curable o eric Polymer of CBFB/CFICH? in diisobutyl ketone is polymer was dispersed throughout the continuous completely transparent. Similarly a film cast from a Iphaseofthech|rine freepo1ymer Solution of an elastomeric Copolymer of CF, In addition to the ingredients'listed in Table 1, formu- CFCl in diisobutyl ketone is completely transparent. lations l-'-4 contained 30 parts by weight of carbon However, mixing the above two solutions together and black as a reinforcing pigment for the elastomeric then casting a film therefrom leaves a translucent film p y The carbon black used was a which indicates that these two polymers are not mu- "adename P nyJ"- tually soluble at room temperature. Formulations 1-14 also contained 1 part by weight of The largest use of the fluoroelastomer combination h f by weight of f of the invention is for O-rings, gaskets, shaft seals, Part by w h of sleeves, etc. Therefore, the blended polymers must be N cured before they can be so used. The curing process typically comprises two steps. The first step is the (C4H)4N+|:S*C :l pressing of the fluoroelastomer compounded disper- S sion into a mold and heating (press cure). The press T'fi i di i di i to the Mg() d cure is conducted at a temperature between about 275 Ca(OH),, comprised the curing system for the F. (135 C.) and about 400 F. (205 C.), preferably chlorine-free polymer. The curing system for the between aboutv 300 F. (150 C.) and about 345 F. 5 chlorine-containing polymer included MgO and hex- (175 C.) for a period of from 5 minutes to about 1 amethylenediamine carbamate- 7 hour. A pressure f between about 7 and about 210 The silica used was a finely divided colloidal silica kg/cmz, and preferably between about 3 5 and about 70 such as Hi-Sil 223", a trade name of Pittsburgh Plate kg/cma, is imposed on the compounded dispersion of Glass Silica is a preferred, reinforcing agent for the polymers in the mold. The press-cured elastomer is chlormefiomammg polymer" then removed from the mold and placed in an oven for zmc sitearate was 7 as 7 pmceiwimg posbcuring ormulatlon 15 comprised,- in addition to the mredients stated inTable I 10 parts of zinc oxide (a The press-cured elastomer must have sufficient g common substitut f r strength and toughness to resist tearing or breaking e o magnesmm oxide) 10 parts of dibasic lead phosphite, 2.5 parts of DiakNo. l (a under the stress required to remove it from the mold. blocked amine f DuPont) and 10 parts f diisobutyl elastomerlc polymers, wherein the chlorine-containing The ability to so resist tearing or breaking is expressed k t processing aid) This f m l i was herein as Press cure tear prepared by blending all of the noted ingredients The molded fluoroelastomer IS usually post-cured together on atwo roll rubber mill.

TABLE I v Formulamn 1 2 3 4 5 6 7 s 9 10 11 12 v 13 14 15 In edients, parts by Weight:

(75/25) CFzCHz/CFzCFCl (/50) CFaCI-h/OFzCFCl (/35) Silica I Table VI Continued mama A 1 7 I f j l 0.; "0.5 :23131: Ilexatnethylene diamine curbamate 0. 08 0. 1 '0. 1 0. 1 0. 2 0. 8 0. G *0. 6 0.8 0. 25 0. 25 lress.cure (20 min/168 I v C.) Hardness Shore A 65-72 65 72 65 65 65 65 60 60 69 64 I 64 v 64 Oven-cure (24 hrs/260 C.) 'llard'ne'ss Shore A... 72-80 73 78 78 74 76 76 77 76 t 76 76 30 Press cure tear strength,

,kgjvin 10-11 19 13 20 19 26 29 30 25 27 15 23 27 3!) 36 Oven cure tear st ongth,

kgJcm v ,4 13-14 14 12 1 1 16 19 14 17 18 18 I 34 OVvn euro uttlllli" (7.

The 'tear strength of the fluoroelastomer combina tions was measured in accordance with ASTM Test Method D62454. The tests were run with die C and the tear strength was measured in units of kilograms per centimeter thickness. Generally, a press-cure tear strength of at least about 15 kg/cm is preferred for preventing tearing or breaking vof the fluoroelastomer article when removing it from the mold.

EXAMPLE II Fluoroelast'omer combinations made from the formulation shown in Table [I were prepared according to two different methods to show that prolonged or unnecessarily extended milling of the chlorine-containing polymer with the chlorine-free polymer is not needed, nor is it particularly desired when greatly improved tear strength is sought. For each method of preparation,the ingredients which are marked with an asterisk were first blended together as a pre-mix and the remaining ingredients were blended'together as another pre-mix. The two-pre-mixes were then blended together on a tw'o-roll rubber mill.

According to one method of preparation, the

premixes were blended together'using alarge two-roll rubbermill with tight clearance between the rolls.

After the pre-mixes were thoroughly blended in the center one-third area of the rolls, cutting and banding was'continued for about 30 minutes. Samples of the fluoroelastomer combination were then press cured and oven cured. The sampleswere tested in a manner similar tothat used in Example l. The results were-as follows:

Tear strength:

Press cure (20min./l 68 C.) 26 kg/cm Oven cure (24 hrs/260 C.) 20 kg/cm "According to the other method'of preparation, the .pre-rnixes were blended together using a small two-roll rubber mill with loose, clearance between the rolls. The pre-mixes were blended together until it appeared that the chlorine containing polymer had been adequately dispersed throughout the chlorine-free polymer. The

combination were then press cured and oven'cured, after which the samples were tested in a manner similar to that used in Example I. The results were as follows: Tear strength:

Press cure (20 min/168 C.) 31 kg/cm Oven cure (24 hrs/260 C.) 36 kg/cm Although both of the resulting fluoroelastomer combinations described in this example are within the scope of this invention, the preferred results are obtained when prolonged milling of the chlorine-containing polymer and the chlorine-free polymer is avoided. The polymers generally should not be milled together for a time longer than is needed to obtain a fairly uniform dispersion of one polymer throughout another polymer.

EXAMPLE III A fluoroelastomer combination .was

prepared using the ingredients of Table III.

The method by which the ingredients were blended was the same as that-describedin Example pilwith the small two-roll rubber mill. After the polymers were adequately blended, the resulting dispersion .was

removed from the mill to avoidprolongedmilling.

Samples of the fluoroelastomer combinationl were then press cured and oven cured after-,which they were tested in-accordance with ,thevmethods of Example I. The results were as follows:

Tearstrength:

Press cure (20 min/68C.) 30-kglcm Oven cure (24 hrs/260 C.) 41 kg/cm I Various curing systems may-be used for curing the highly fluorinated .elastomeric polymersused in the fluoroelastomer combinations of the invention.F or example, standard curing systems for the vinylidene fluoride/chlorofluoroolefin elas'tomeric copolymers include peroxides, isocyanates, polyamines and quaternary salts. These curing systems may also be used in conjunction with known fillers such as silica, clay, carbon and-pigments. The use of a peroxide or blocked amine cure in conjunction with silica reinforcing agents I is particularly useful.

Similarly, known compounding systems for vinylidene fluoride/perfluoropropene co'polymers can be used, including curing systems such as peroxides, amines, blocked amines, quaternary salts, aromatic nucleophiles, polyethers etc. These curing systems may be used separately or in combination with each other and they may also be used in conjunction with reinforcing pigments (e.g. carbonblack, silica, clay), colorants, plasticizers, processing aids and the like.

Although it is not necessary to include any silica in the fluoroelastomer combinations of the invention, it is preferred to include from 1 to 40 weight percent based on the weight of the chlorine-containing polymer. When silica is included in the formulation, it is preferred to blend the silica with the chlorine-containing polymer before blending the" latter with the chlorine-free polymer.

What is claimed is: w

l. A thermally stable, chemical-resistant fluoroelastomer combination of improvedprocessing and handling properties comprising at least two highly fluorinated curable elastomeric polymers containing at least 37 percent by weight of carbon-bonded fluorine, one of said polymers being a chlorine-free polymer and the other'of said polymers being a chlorine-containing a continuous phase and the other of said-polymers is in-' polymer represents about 3 to 97 weight percent of said polymer, wherein one of said polymers is in the form of fluoroelastomer. combination, said chlorine containing polymer being an elastomeric vinylidene fluoride/chlorotrifluoroethylene' copolymer.

2. A thermally stable, fluoroelastomer combination in accordance with claim 1, wherein said elastomeric polymers are cured.

3. A thermally stable, chemical-resistant fluoroelastomer combination in accordance with claim 1, wherein said fluoroelastomer combination'contains.

3 to 30 weight percent chlorine-containing polymer dispersed throughout a continuous phase of chlorinefree polymer. 1

4. A thermally stable, chemical-resistant fluoroelastomer combination in accordance with claim 1, wherein said fluoroelastomer combination contains about 3 to 40 weight percent of chlorine-free polymer dispersed throughout a continuous phase of chlorinecontaining polymer.

5. A thermally stable, chemical-resistant fluoroelastomer combination of improved processing and handling properties comprising at least two highly fluorinated elastomeric polymers, one of said polymers comprising a major amount of an elastomeric vinylidene fluoride/perfluoropropene copolymer, and

another of said polymers, whichrepresents about 3 to 97 weight percent of said fluoroelastomer combination,

comprisin a major amount of an elastonieric vinylidene ffiioride/chlorotrifluoroethylene copolymer, wherein one of said polymers is dispersed throughout, and soluble in, another of said polymers.

chemical-resistant- 

2. A thermally stable, chemical-resistant fluoroelastomer combination in accordance with claim 1, wherein said elastomeric polymers are cured.
 3. A thermally stable, chemical-resistant fluoroelastomer combination in accordance with claim 1, wherein said fluoroelastomer combination contains 3 to 30 weight percent chlorine-containing polymer dispersed throughout a continuous phase of chlorine-free polymer.
 4. A thermally stable, chemical-resistant fluoroelastomer combination in accordance with claim 1, wherein said fluoroelastomer combination contains about 3 to 40 weight percent of chlorine-free polymer dispersed throughout a continuous phase of chlorine-containing polymer.
 5. A thermally stable, chemical-resistant fluoroelastomer combination of improved processing and handling properties comprising at least two highly fluorinated elastomeric polymers, one of said polymers comprising a major amount of an elastomeric vinylidene fluoride/perfluoropropene copolymer, and another of said polymers, which represents about 3 to 97 weight percent of said fluoroelastomer combination, comprising a major amount of an elastomeric vinylidene fluoride/chlorotrifluoroethylene copolymer, wherein one of said polymers is dispersed throughout, and soluble in, another of said polymers. 